The present invention relates to a gas mixing device capable of forming a gaseous mixture of a predetermined mixing ratio and to a gas analyzer having such a gas mixing device.
The specification of the U.S. Pat. No. 3,464,434 discloses a device capable of continuously mixing two or more gases. This known art employs elongated tubes serving as flow resistance passages. Two or more different gases are introduced through the respective elongated tubes and are made to merge with each other so as to form a gaseous mixture. On the other hand, in the field of analyzers for measuring blood gases, a plurality of gas-containing standard liquids or a plurality of standard gases are used for the purpose of calibration. The preparation of the gaseous standards is conducted by extracting carbon dioxide, oxygen and nitrogen gases from the respective cylinders, allowing these gases to merge with each other and then bubbling the thus formed mixture through an aqueous solution. This type of art is disclosed in, for example, Japanese Patent Unexamined Publication No. 61-200458 corresponding to the U.S. Pat. No. 4,696,183. The present inventors have attempted to make use of the method disclosed in the U.S. Pat. No. 3,464,434 in the preparation of the standard liquid for blood gas analyzer. In this attempt, elongated tubes of stainless steel were used as the flow resistance tubes. Unfortunately, however, it is difficult to obtain a constant inside diameter over the entire length of the stainless steel tube. This makes it difficult to set the resistance value within a predetermined range of error. Thus, a predetermined resistance valve is obtained by cutting a steel tube to a length greater than a calculated length, measuring the flow resistance therethrough and thereafter repeating the process until the predetermined resistance value is obtained. The gas mixing device thus formed is large in size and heavy in weight.